1. Field of the Invention
The invention relates to the pumping of highly viscous materials such as plastics of the type having a base of butyl rubber and/or polyisobutylene and exhibiting a viscosity greater than 35,000 poises (3500 Pa.multidot.S). Being suitable for the pumping of highly viscous materials, with a viscosity greater than 35,000 poises, the invention is also suitable for the pumping of materials exhibiting a lower viscosity.
2. Discussion of the Related Art
Reciprocating vane pumps driven by a pneumatic means, able to pump relatively slightly viscous materials, and permitting a maximum viscosity on the order of 35,000 poses are known. Thus, polysulfide which has a viscosity of 35,000 posies represents, from the viewpoint of viscosity, the limit of what the known reciprocating vane pumps can pump.
These pumps are driven pneumatically; they are provided with narrow passages practically without clearance, in particular at the position of the ring-shaped check valves mounted around the rod which carries the vane, and they have narrow ports of 5 mm.sup.2 or less for the passage of the material to be pumped.
These pumps prove to have absolutely zero effectiveness for pumping materials of the type having a base of rubber butyl and/or polyisobutylene with a molecular weight on the order of 8,000 to 15,000 (according to STANDINGER), these materials having a viscosity which, expressed in Mooney degrees, is on the order of, or greater than, 115.degree. at the end of eight minutes and at a temperature of 40.degree. C. (measurement made with a Mooney consistometer according to the recommendation ASTM D 1646-74).
Actually, these materials having a base of rubber and/or polyisobutylene, and other materials of the same consistency, are too thick for the vanes of these pumps to succeed in penetrating them. Increasing the power of the motor of the pumps to press the vane with more force has been tried, but the rod which carries the vane then deforms laterally and is locked in the narrow passages where it slides, in particular in the check valves which surround it like a ring. If the power is further raised, the rod wears and forms shavings by rubbing against the walls of said narrow passages and in particular of the ring valves.
Reinforcing the rod by increasing its section has been tried, but it was also necessary to increase the size of the other elements of the pump and consequently at the same time the power of the motor. Huge pumps thus resulted and the power thus used were such that the tanks into which it was desired to pump the material were no longer strong enough to absorb the pressure to which they were subjected, with the result that they burst.
In the face of the complete ineffectiveness of these reciprocating vane pumps to pump high-viscosity materials, a device described in French Patent Applications published under the Nos. 2 567 448, 2 570 322, 2 570 443, 2 570 324, 2 570 323, was resorted to for feeding of a thick plastic having a butyl rubber and/or polyisobutylene base of molecular weight on the order of 8,000 to 15,000, together with an extrusion head intended to furnish a bead of said plastic able to be used as a seal and interlayer between two consecutive sheets of glass in multiple glazings.
This unit uses a concial plate equipped with heating appendages and provided with a port at the conically shaped vertex through which the material is extracted. This plate is pressed with force against the plastic contained in a tank. The heat and the particular shape of the plate cause material to be extracted through the port for feeding an internal gear pump. This gear pump causes the material to advance in rigid pipes connected, via rotary seals, to a variable volume storage bin placed immediately upstream from the extrusion head. At the position of the gear pump, the flow is still slight and the material is still thick, with the result that to obtain a sufficient flow to prevent damaging the gears of the pump and the drive system, said pump is fed simultaneously on both faces of the gears, the teeth of the gears are trapezoidal and the drive of said pump is hydraulic.
With these devices, plastic of the type having a butyl rubber and/or polyisobutylene base of molecular weight of 8,000 to 15,000, was extracted from the tank where it is stored at a sufficient flow rate and with a sufficient consistency to feed an extrusion head and continuously produce multiple glazings of large dimensions (about 10 m of maximum perimeter), with an interlayer bead of said plastic separating two consecutive sheets of glass, and forming a seal between said two sheets of glass, by a height that can go to 12 mm, the sheets of glass passing under the extrusion head at speeds on the order of 20 m/min, i.e., with a flow on the order of 1 kg per minute. However, this unit for preparation and extraction of the plastic nevertheless poses problems.
Actually, the material exits at a high temperature on the order of about 130.degree. C. This temperature is due to the heating occuring at the conical plate, but it is also due in large part to the shearing that the material undergoes in the gear pump. This high temperature at which the plastic is supplied can be harmful. Actually, if this material is extruded at too high a temperature, the bead obtained is too soft and has a tendency to creep and to collapse under its own weight. It is then necessary to provide means to support it as soon as it is placed on a sheet of glass, in particular if it has a great height. Such means are, for example, described in French Patent Application No. 84-14185.
Furthermore, for other applications, in particular in the field of automobiles, a need is felt for pumps able to pump thick plastics, optionally without it being necessary to heat them too highly, and so far, this need has not been met.